I do my overhaul and tuning myself, but since you are using Honda and if you need to, just go to AHASS service, the official Honda service point. Their workshop building looks like this.
They have fixed price and certificated engineers and since there is no modification on postie's engine, you can count on their original Honda spare parts if you need to replace something, since its spare parts are same with astrea series and supra series.
You can find such workshops everywhere in town everywhere in Indonesia.
Postie is categorized as small bike. Complete tuning including the original Astra Lube 4000km Lubricant Oil should be no more than 100k rupiahs at most.